[filmscanners] RE: Newish Digital Tech

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

> From: Austin Franklin
>
> I am only somewhat familiar with how PMTs operate, but I do know
> the ones I’
> ve seen use a beam splitter of some sort...but why would a PMT get “more”
> light, or not be subject to the same issue you raise above about
> columnation
> of “signal”?  It appears to me they would.  I’m not talking about sensor
> noise, but simply photon noise.  If you could explain why you
> believe that I
> ’d appreciate it.

I'm no expert in physics, but as its been explained to me, PMTs are
multi-stage devices that are biased as sensitive triggers, so that each
photon that strikes the first electrode kicks off one electron, which causes
a phosphor to emit a few photons, which strike the next electrode, causing
it to dislodge a few electrons, which generate more photons, and so on down
the stages. In semiconductor sensors, however, many, perhaps most, of the
photons that hit the junction do absolutely nothing, so they're much less
sensitive. Photodiodes are better, as they manage to capture (I believe) all
the photons that strike them, but they don't have the built-in amplification
of the PMTs.

I don't know if anyone has made any progress in manufacturing arrays of
microscopic photomultiplier devices for capturing light, but they do
something similar in high-speed analog oscilloscopes for increasing the
amount of light generated as an electron beam sweeps by at a very high
speed.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com

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